When was the last time the right-ctrl key was working properly? Seems odd, it could be a wiring fault that's suddenly occurred (did you drop any drinks or anything into the keyboard?). Other than that... if it's a config thing it would probably have to be a physical switch you flipped somewhere, it seems really unlikely the keyboard on a laptop would have such a switch.

I don't remember anytime specific that I used the right control key as opposed to the left, but I use keyboard shortcuts prolifically (and often while walking around with the laptop, so one hand is gripping the laptop and the other is pressing the shortcut) so I can't imagine it will have been more than a day or two, possibly even less.

I haven't dropped any drinks on it, and I would imagine such a thing would affect more than just the one key. But I do have four kids and god only knows what they get up to when I'm not around.

I can't imagine such a config item either. If it is a wiring fault, what are the chances it'll fix itself or I can find a way to fix it?